Whereas in an aromatic molecule there is continuous overlap of p-orbitals over a cyclic array of atoms, in a homoaromatic molecule there is a formal discontinuity in this overlap resulting from the presence of a single sp3 hybridized atom at one or several positions within the ring; p-orbital overlap apparently bridges these sp3 centres, and features associated with aromaticity are manifest in the properties of the compound. Pronounced homoaromaticity is not normally associated with neutral molecules, but mainly with species bearing an electrical charge, e.g., the "homotropylium" cation, C8H9+,
In bis, tris, (etc.) homoaromatic species, two, three, (etc.) single sp3 centres separately interrupt the pi-electron system. See also homoconjugation (2).
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